Load balancing system



Jan. 31, 1950 Filed Dec. 18, 1947 E. M. SQRENSEN LOAD BALANCING SYSTEMRECTIFIER 2 Sheets-Sheet l RECTIFIER R EGU L ATOR RECTIFIER LOADRECTIFIER REGULATOR 3 PHASE RECTIFIER ALTERNATOR TRANSFORMER VOLTAGE 15REGULATOR REC IFIER LOAD RECTIFIER VOLTAGE REGULATOR A RANSFORMER 3PHASE ALTERNATOR RECTIFIER A TTORNEY Jan, 31, 1950 M '$ORENSEN 2,495,783

LOAD BALANCING SYSTEM Filed Dec. 18, 1947 2 Sheets-Sheet 2 c, RECTIFIER8 19 To REGULATOR 15 2 I; 241 3 1 IN V EN TOR.

[fin/APO M JOAEA/Sf/ 05654550, '2 BYl/ELF/V s, seem/am; Adm. REGULATORjJBY ATRECTIFIER 81 I A TTORNE Y Patented Jan. 31, 1950 LOAD BALAhiCINGSYSTEM Edward M; Sorensen, deceased, late ofStamfoi-d,

Conn, by Helen S. Sorensen,

administratrix,

Stamford, Conn., assignor to Federal Telephone and Radio Corporation,

poration of Delaware New York, 'N Y., a cor- Appiication December 18,1947, Serial No. 792,479

Ti This invention relates to electrical load-balancing systems adaptedto maintain an equal load nators driven from separate motors are eachconnected through a transformer rectifier regulator systemto the samedirect current circuit. It hasbeen found that in apparatus of this typethere is a tendency for one unit to assume more of the load than theother, a condition that may result in placing substantially all of theload on that unit.

i The general purpose of the invention is to provide a system suitablefor automatically maintaining equal loads on both supply systems. Anobject is to provide an automatic load-balancing unit adapted to correctunbalanced load conditions by automatically adjusting a voltageregulator, and a feature thereof is the provision ofa unit of'this typethat can be readily applied to voltage regulators.

I A specific purpose is to make the required adjustment of the voltageregulator by changing the value of a variable impedance ntherein whenthe load is unbalanced, thereby 1 changing the output voltage from thevoltage SOUICGLtO which the regulator is coupled- The resulting changein voltage is appropriate for increasing the load on the less loadedsource, and

is automatically terminated by restoring said impedance to its normalvalue when the sources are equally loaded.

Another object of the invention is the provision of a simple, compactand light automatic balancing system of the indicated type. Thearrangement is especially suitable for the use of electric metalrectifier units, which have the requisite size and lightness.

Other objects and advantages will appear from .the followingdescription, considered in conjunction with the accompanying drawings,in which:

1. Figure 1 illustrates in block form the basic arrangement of aproposed load-balancing system;

'1 -Fig. '2 is a partially block and schematic diagram of one preferredembodiment constructed in accordance with the present invention;

Fig. Bis a circuit diagram of one form of the arrangement shown in Fig.2; and

Fig. 4 shows a portion of an embodiment of this invention utilizingpolarized relays.

Fundamentally, the proposed arrangement for load-balancing may berepresented by the dis- 2 Ciaims. (01. 171419),

closureof Figure 1, in which a load I' is common to a pair of paralleledrectifiers 2 and 2', each in turn receiving power from separate A.-C.transformers 3 and 3' respectively. Coupled with rectifier 2 is aregulator 4, and with rectifier 2' another regulator 4. These twocombinations of the rectifiers and regulators provide means foradjusting the A.-C. voltage applied to the rectifiers such that outputto the load is substantially constant and such that the outputs of bothrectifiers are substantially equal. Additional rectifiers, 5 and 5',which do not see the actual load, are coupled with the A.-C. inputs ofrectifiers 2 and 2 respectively and also with regulators 4' and 4respectively. These rectifiers 5 and 5' are utilized to maintain a loadbalance when unbalance conditions arise. In the event that one ofrectifiers 2 and 2 has more load than the other, there will be adifference in potential at the outputs of transformers 3 and 3. Theinterconnections of rectifier 5 with regulator 4 and rectifier 5' withregulator 4 impress the rectified transformer output voltages upon theseregulators in serieswith the voltages from the regulators 2 and 2' suchthat the regulators may change the transformer primary voltages untilthe load is shared equally by the last-named rectifiers.

Referring to Figure 2, the invention is illustrated as applied toalternating current generating units provided with suitable transformersand rectifiers, the direct current outputs being connected in parallelto the common load I The upper unit comprises a three phase alternator6, connected to transformer 1 whose output passes through rectifier 8,the direct current output of which is connected to load I throughpositive conductor 9 and negative conductor l0. Conductors 9 and [0 areconnected through leads II and I! to voltage regulator l3, which isactuated by variations in the potential difference between the latterleads. The lower unit is of similar type, and the corresponding partsare indicated by the same numerals with primes.

Regulator I3 may be selected from various types. It may be of the typewhich changes the transformer ratio 5 in the transformer unit 1, systemsof this type being illustrated in the pending application Ser. No.499,034, filed August 18, 1943. The regulator may likewise be of thetype that varies the voltage of the output of alternator 6. Varioustypes of regulators acting on the alternator circuit are known,including the carbon pile, vibrator and others. Voltage regulators ofthese types include generally a resistance whose value determines thenormal alternator output voltage; and a change in the value of suchresistance will produce a corresponding change in the normal voltage.The regulator may include an inductance which performs a similarfunction, and the normal voltage may be changed by varying the value ofthe inductance. Connections either to transformers 1 and l -oralternators 6 and 6 are represented by the switch connections 3a, l3band 13a and I31), Fig. 2.

The present invention is adapted to correct an unbalanced load bychanging the value of such' resistance or inductancer and this isconveniently accomplished by short-circuiting a portion thereof having avalue suitable for producingthe requisite shift in the normal voltage.

In the illustrated arrangement this is accomplished by connecting abalancing rectifier to the output of transformer l. The positive leadfrom rectifier i4 is connected to the positive side of blockingrectifier element I5, the negative side beingconnected to the -windingof relay 56, ,the

other terminal of which is connected through lead ilto the positiveoutput side of the lower balrectifier l4 and to the voltage regulatorl3. The

voltage regulator 53 includesa; resistor 19, whose function is describedabove, one-end; of the re sistor being negative and ordinarily connectedto .the lead l2. Armature i8 is ccnneeted through leadit to apointonlresistor i9 adjacent said negative end, the arrangement being suchthat when-armature i8 is closed, a portion at the positiveend-of theresiston-iS-willbe short-circuitcd thereby lowering the valueofsaidresistoiz. A

similar-arrangement is connected to relay W and voltage regulator i3",and is indicatedbythe same numerals with primes.

When-the described system is in normal operation withequal loads onbothgenerators; and 5, the voltage dro across the outputs of transformerl the balancing rectifier, EA will be the same as that across theoutputs of-transforrner l and balancing rectifier, it. Consequentlythere will be no potential difference between the positive terminals ofsaid balancing rectifiers and no currentwill flow between saidterminals. Uri

the e conditions relays ifiand lfiflwill remain open and thevoltageregulators l3 and l3- will operate in normal manner.

If, however, the load tends to shift to generator 6, the greater currentfiowthrough-transformer 'i will create a greaterdrop in potential acrossthe output terminals of the trans former and those of balancingrectifier M, while the lowered current flow in the output of transformerT will reducethe potential drop across, the output terminals ofbalancingrectifier M. Under thesev circumstances the positive terminalof rectifier id will be negative with respectto the positive terminal ofrectifierl4, and current will flow through rectifier element l5 andrelay 16, it being prevented from flowing throug relay it by blockingrectifier element 15. Annature i8' will close, reducing theyalueof;resis.tor

l9 and causing regulator l3 to increase the outp rolie ie senereie 7-.fl iwil eqf gees 4 tend to take part of the load from generator I. Assoon as the load on the latter generator has reached a point where thecurrent flow in the output of transformer I is substantially the same asthat in the output of transformer I, the potential difference betweenthe positive terminals of balancing rectifiers, l4 and ll willdisappear, causing armature 18 to open and restoring the resistor i9 toits normal value.

A similar operation occurs when a predominant portion of the load isshifted to generator 6, in which case current will flow throughrectifier ele .ment [5 andrelay l6, increasing the output volt- .age ofgenerator 6 until the loads are balanced. The provision of theoppositely directed blocking rectifier elements [5 and IS in theparallel circuits between the positive terminals of balancing rectifiersi4 and E4 is effective in selectively actuating the voltage adjustingapparatus, consisting of relays l6, l6 and their connections, to pr ducthe. de i d oed s t chan en t .mr pe dire tion- Q e'.-spcci c mbo imenofrt isa r ns mc is; disclosed-in Fig. 3 ;and is i n generalself-exusual three; phase full wave; type, and are ,Par-

.ticularly suitable for the pee of selenium rectifiers. {The voltageregulator, 13 I is, of p the 1 carbonpile type in ,whicha carbon pileresistor; 2 1;, in series, wit hsaturable core reactors 22 ,in the 1primary .leads of transformer-:1, is-varied inactcq 'da c wit u renchanc s; n the arbo conflpressing solenoid 2 3 connectedto positive deadii, theresistor. (9 also being inseries therewith. 'Vfjhilethe carbonpile Zl is shown in series with the reactors 22, and various features ofthe --;i .i a c rbon pi v l a c n c ns ruc ave been oipitted, thishasbeendone forthe sai-ze ;of clarity, since such ,arrangementspyaretandardland jwell known. T;he= same vregulator angement is shown inconnection .withgener- 11cm? 61 and nd c t di y sim l n um ra slw:rrimes tialshowing of; the SYStBlllOf- Figure 2. The, out- --puts; ofeach of the rectifiers; 8 and- 8' are icon- -nected toa pair of relaycoils,-one of'the.--,P ir hegtwo Polarized -relays generally designatedby numerals land 24. Qoupled to. rectifier 8 ,are the relay, ,coil' 25 1on core 3B, of. polarized relay; 24 and relay coil 25' oncorefi' ofrelay 24. :vsilnilarlm coupled to rectifier 8' are relay coils 21and;2l'-,,on cores," and jfi; respectively. Should anyavoltageunbalance; occurin the volta e output of the recti- .fiers; 8 ,and 8,the coils onboth of theirelaycores will produce unbalanced magneticefiectsand cause the relay, armature 28 and-18' to. beattracted tocertain positions. Fonexamplewhen ;the;output of rectifier; 8' is the.greater, currents vflowing inrelaycoils 2i. and 21. willexceedthoseflowing in;25 and;25,-creating a magnetic unbalance in-cores, Hand 26'which is sufficient to close armature 2%! with contact 29, thus shortingout a; portion-of resistance 19,, and insuring that relayarmature; 28will not,- be attracted ,to close with contact; 2 9 ;The reverse. actionoccurs when thejoutput-yoltage of rectifier. 8.is larger "than that ofrectifier 8. Begulator'operation in theselnstanc es .isthe same es-previously described with regard to the; other embodiments. iAlthoughthe embodiments herein described are whichever rectifiercontributes the smaller part of the load current, it may be desirable incertain applications to achieve the reverse, that is, reduce the outputof the other rectifier until the rectifier having the lesser outputvoltage assumes its proper share of the load. To accomplish this, anarrangement opposite to those shown might be employed wherein the relayexcitations open normally closed relay switches to insert higherimpedances into the regulator circuits.

It will be apparent that the disclosed balancing arrangement is adaptedfor construction as a very light and compact unit, using seleniumrectifiers having only a sufiicient output to operate the relays, whichmay be small and simple in type. The balancing system can be applied tovoltage regulators of the various types indicated simply by connectingit to the proper transformer and rectifier leads, and connecting leads20, 20' to appropriate points on the impedances l9, 19'. The control maybe made sufiiciently sensitive without danger of excessive huntingaction by providing relays which have a suitable difference between thevoltage at which they close and that at which they open.

It is claimed:

1. An electrical load-balancing system for parallel current supplysources, each source including a source of alternating current and arectifier for said current, the rectifiers being arranged for connectionin parallel to a common load comprising means for regulating the voltageof the alternating current from said source, a control rectifierconnected across the alternating current output from each source, andmeans connected in series between the control rectifiers, responsive todifferences in the potentials of the outputs of said control rectifiersdue to unabalanced loads, for actuating the regulating means toeliminate said differences in potential, said actuating means comprisingrelay means and switch means actuated by the relay means when energizedto change the adjustment of the regulating means.

2. A load-balancing system as set forth in claim 1 in which theactuating means comprises two relays connected in parallel betweensimilar output terminals of the control rectifiers, a rectifier elementin series with each relay, said elements being connected in oppositesenses so that current flowing between the control rectifiers in eitherdirection will pass through only one relay, and switch means associatedwith each relay, actuated when said relay is energized, for changing theadjustment of the voltage regulating means and thereby eliminatingpotential difierences between the control rectifiers.

HELEN S. SOREN SEN Administratrz'r of the Estate of Edward M. Serensen,Deceased.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

